1. Field of the Invention
The present invention relates to an automotive display apparatus which reflects a display image of an indicator by a reflection surface located in front of the driver's seat so that a driver can see the display of information on vehicle running conditions such as car speed within a viewing field of the windshield.
2. Prior Art
The apparatus of this kind is generally called a head-up display, which is designed to reduce the shift of the driver's line of sight when the driver checks the car speed while driving. The apparatus reflects the display image of an indicator showing such information as the vehicle speed toward the driver's seat using the inner surface of the windshield to form a virtual image of the display within a viewing field of the windshield when viewed from the driver.
During high-speed driving, a driver looks far ahead. To reduce the amount of focus shift of the driver's eye when he or she checks the display, it is a conventional practice to provide a so-called remote display, in which a virtual image of the indicator display, when viewed by the driver, is formed at a location remote from and in front of the windshield.
FIG. 6 shows one example of a prior art display apparatus or a head-up display apparatus which produces the above-mentioned remote display. In the figure, reference numeral 1 represents a windshield, 2 a dashboard, 3 an indicator unit, and 4 a viewing point of a driver. This apparatus reflects a display image of the indicator unit 3 installed in the dashboard 2 onto the windshield 1 toward the driver's seat so that the driver can see, from the viewing point 4, a virtual image X of the display within a viewing field of the windshield 1.
As shown in FIG. 7, the indicator unit 3 contains an indicator 31 such as a fluorescent display tube, a plane mirror 32 and a concave mirror 33, all arranged in their specified optical positional relationship. The display image of the indicator 31 is reflected by the plane mirror 32 toward the concave mirror 33, which further reflects it toward the windshield 1.
The indicator 31 is located within the focus of the concave mirror 33, which enlarges the display image so that the distance L from the windshield 1 to the virtual image X is longer than the light path .alpha.+.beta.+.gamma. extending from the windshield 1 to the indicator 31 through the concave mirror 33 and the plane mirror 32. If the concave mirror is not used, it is impossible to secure a light path long enough to produce a satisfactory remote display by only the reflections inside the indicator unit 3 since the indicator unit 3 is installed in the dashboard 2 and thus cannot be allocated a large space. To solve this problem, the concave mirror 33 is employed to enlarge the display image and thereby form the virtual image X at a remote position.
In the above-mentioned conventional apparatus, however, the remote display is formed by a single concave mirror 33, making it necessary for the concave mirror 33 to have a large magnifying power. This results in a distorted virtual image X and also gives rise to the problem of the visual field of the concave mirror 33 being reduced, thereby narrowing the effective range of the display image that is magnified by the reflection surface of the concave mirror 33.